938,448 research outputs found
DNA as a universal substrate for chemical kinetics
Molecular programming aims to systematically engineer molecular and chemical systems of autonomous function and ever-increasing complexity. A key goal is to develop embedded control circuitry within a chemical system to direct molecular events. Here we show that systems of DNA molecules can be constructed that closely approximate the dynamic behavior of arbitrary systems of coupled chemical reactions. By using strand displacement reactions as a primitive, we construct reaction cascades with effectively unimolecular and bimolecular kinetics. Our construction allows individual reactions to be coupled in arbitrary ways such that reactants can participate in multiple reactions simultaneously, reproducing the desired dynamical properties. Thus arbitrary systems of chemical equations can be compiled into real chemical systems. We illustrate our method on the LotkaāVolterra oscillator, a limit-cycle oscillator, a chaotic system, and systems implementing feedback digital logic and algorithmic behavior
Quantum Indistinguishability in Chemical Reactions
Quantum indistinguishability plays a crucial role in many low-energy physical
phenomena, from quantum fluids to molecular spectroscopy. It is, however,
typically ignored in most high temperature processes, particularly for ionic
coordinates, implicitly assumed to be distinguishable, incoherent and thus
well-approximated classically. We explore chemical reactions involving small
symmetric molecules, and argue that in many situations a full quantum treatment
of collective nuclear degrees of freedom is essential. Supported by several
physical arguments, we conjecture a "Quantum Dynamical Selection" (QDS) rule
for small symmetric molecules that precludes chemical processes that involve
direct transitions from orbitally non-symmetric molecular states. As we propose
and discuss, the implications of the Quantum Dynamical Selection rule include:
(i) a differential chemical reactivity of para- and ortho-hydrogen, (ii) a
mechanism for inducing inter-molecular quantum entanglement of nuclear spins,
(iii) a new isotope fractionation mechanism, (iv) a novel explanation of the
enhanced chemical activity of "Reactive Oxygen Species", (v) illuminating the
importance of ortho-water molecules in modulating the quantum dynamics of
liquid water, (vi) providing the critical quantum-to-biochemical linkage in the
nuclear spin model of the (putative) quantum brain, among others.Comment: 12 pages, 5 figures. Clarified presentation and figure
Modeling and simulating chemical reactions
Many students are familiar with the idea of modeling chemical reactions in terms of ordinary differential equations. However, these deterministic reaction rate equations are really a certain large-scale limit of a sequence of finer-scale probabilistic models. In studying this hierarchy of models, students can be exposed to a range of modern ideas in applied and computational mathematics. This article introduces some of the basic concepts in an accessible manner and points to some challenges that currently occupy researchers in this area. Short, downloadable MATLAB codes are listed and described
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